From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 78B53606A327 for ; Sun, 15 Nov 2026 06:05:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=chrisdown.name header.i=@chrisdown.name header.a=rsa-sha256 header.s=google header.b=b+M7nknD Received: by kanga.kvack.org (Postfix) id 86EAF6B05B0; Sun, 15 Nov 2026 01:05:37 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7F7C16B05B1; Sun, 15 Nov 2026 01:05:37 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 70E3F6B05B2; Sun, 15 Nov 2026 01:05:37 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 3CADE6B05B0 for ; Sun, 15 Nov 2026 01:05:37 -0500 (EST) Received: from smtpin01.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id A70B9A03EC for ; Sun, 15 Nov 2026 06:05:36 +0000 (UTC) X-FDA: 85436316672.01.D75F518 Received: from mail-dy1-f171.google.com (mail-dy1-f171.google.com [74.125.82.171]) by imf31.hostedemail.com (Postfix) with ESMTP id C0F2020004 for ; Sun, 15 Nov 2026 06:05:34 +0000 (UTC) Authentication-Results: imf31.hostedemail.com; dkim=pass header.d=chrisdown.name header.s=google header.b=b+M7nknD; spf=pass (imf31.hostedemail.com: domain of chris@chrisdown.name designates 74.125.82.171 as permitted sender) smtp.mailfrom=chris@chrisdown.name; dmarc=pass (policy=quarantine) header.from=chrisdown.name ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1794722734; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=oMjYG3/Fyza/CbXoIQUPnk8H85cPMajtM8cpJ9BN7sY=; b=hIaNHu8RlDI3kmK3U+zPresWhYbpfg3vDD0wELAsTgWP3o4ssGN+SzoBbvKp81v8YPhjVZ kOi+hOmsfw13QCrMgbi58qrNNAZyUFEJvx/dmb1spXrtQpbyhgHpqJIqk2LKiO9Eusvahy wIVeSYVDX4efeZHtawk75caRQViAJC4= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1794722734; b=rswu6bfDMBQWaRsPnpIjXLRWsvzp0A8Q0Xbw+Y+HWSjWptzO7GGrlMqFhNROLyvSIzwXFA YyYehT0YJF6JiF/4tfotQM8jfUlBJlnYeL+gTg1KksX4vvbUII68doyUIJDU6IXF0B4Vpz DnQjmmNRAet60Nx1RBXTKCO/Pxz861Q= ARC-Authentication-Results: i=1; imf31.hostedemail.com; dkim=pass header.d=chrisdown.name header.s=google header.b=b+M7nknD; spf=pass (imf31.hostedemail.com: domain of chris@chrisdown.name designates 74.125.82.171 as permitted sender) smtp.mailfrom=chris@chrisdown.name; dmarc=pass (policy=quarantine) header.from=chrisdown.name Received: by mail-dy1-f171.google.com with SMTP id 5a478bee46e88-37d424f1ae8so783772eec.1 for ; Sat, 14 Nov 2026 22:05:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chrisdown.name; s=google; t=1794722733; x=1795327533; darn=kvack.org; h=user-agent:message-id:content-disposition:content-type:mime-version :references:in-reply-to:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=oMjYG3/Fyza/CbXoIQUPnk8H85cPMajtM8cpJ9BN7sY=; b=b+M7nknDi3CNfn04Cg60DdlgKlRiH3wECAc+SJWyyKbrdT+fjQk9O41ftge2wDdzi+ ls6/v7FyKddYWXNc3/3/vieVPgeLp70xUnBzHpsUBTUzrFizX3OgANDlwZG+mIo0Zxtg K9fbZH3dPwZ3l/2Bm3N8lbYqPvipFqSsu2ldM= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1794722733; x=1795327533; h=user-agent:message-id:content-disposition:content-type:mime-version :references:in-reply-to:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=oMjYG3/Fyza/CbXoIQUPnk8H85cPMajtM8cpJ9BN7sY=; b=eGu31sEwAKPHRFcqzMEshJ0zbPOB5E3Nrur69lqB/W1QhzDNRZ9LXqhhlTAi/BSYfG bfzoLjQvaZi5a5dT+W+McifHjCebe3O9BJQjXNC9F5FJK9RiVCGU5nuowPAflwk/Dvou eP3ARsIzLVHfG395XiqDtPnuB+/oBugc77Cj4CHdyP9rQt+U47AEc8x0KyM/unFZDexn UCahTdd7I4cyLTRud0Qd4jenZjPcdJv/rVS+5wtlPhivwBO8qiYN/F3eJVIUtIzQOyuj 5X0IJOOuZkX/f750LG4b1XD8LCA8JG4l6VrrHDEjddU7yTDwx56DUgojbZWj+FhkBYbg UM5A== X-Forwarded-Encrypted: i=1; AL+hErE3WP/SMkwQi45d+bKjlL+iYtmYwKLuPxuXR7ZHSbzAhQv54Ld4VkIdJBhcqIUjVyN0/JAud/D0/A==@kvack.org X-Gm-Message-State: APuU4Z+VIFy67v/tbBQ4B/Ij52s6+oGe8d6eixEf/XFbaWTyOZM2jY7F qt4/YyP+PnJlyM3b+PHp+DowCOlnISIc//dNbv5Zfl+GoL9cGEkJdUq5wUjWfnhezk8= X-Gm-Gg: AYBFou27IX0fgToeJ1nDDUZYmfy9HK+9SgzazA4HGWsG6BiBXvEqQlQibqPJ7vsQ5vp 8X86BhCh9QXvpS1+9GjZpuTbyBIV/pg3QTLzwtf5QylrlPJkVWXMcxTyDcrxURTu2xJmG0Mto4e QwfqtMZUX1U2c9xRiKNt0riNDKaPBv8L3XvKP/oJERSIABQObEUtRAh1tqwCSgDE7Z0L2Nmlw9O PV4wjoTZH0IBeiG0LHkAv8lwkG4Gtp7AIxYu2BiVPFVKTEYttgSFcj404zzCTh5nTJGrb+O/sPi ow8aUn3MRgRlGUm8s77Zw2TGj1EgGNkjni0eeM2Rt6ywuxJ3MndsMVmEZM3nITTmRhYa8hgqB5B QW/5fL3p31PQdG/zQUzLB9nAklH/7dHaMOf/KR0TRcdUmhSPahi7/ff80aHP9hZhmgHgzlASIar paRNhK+0AnX3+g1R7wWO9GrbbylksYoQo3j4bCOCiV7WVZTIf+NAoCysBpyHnfSMTy/YbA3GElt QxDpJ1D/5ALbePizL2gJx1eqI/lQmzLjZytz3ws+LtjVXZb3NiMEbXQe1uxs0L0Zyv+bXA50G44 xKHDq8Dc2QQpIp8Of6yaciY0x12f8q+3Deh9ciV+GYGuO2MUp/kAAIC0I/6mdZmS6+khTisckAM DqxI0BAU1hDiQC+iUoIw5gueL4+IToOhNCoOU7Ix9TgG46wNk3bYrQQbyfXf5cRKHjQIfZ334zD A3/nFXECL2Fpn9h8/y+yBLVQW/7B1LNm9371N4UJc1rZ+JV6KCEYpaawVPdCdJE8vW X-Received: by 2002:a05:7300:7481:b0:375:c5e1:931d with SMTP id 5a478bee46e88-37966e3aff8mr9995533eec.25.1794722733483; Sat, 14 Nov 2026 22:05:33 -0800 (PST) Received: from [172.18.0.2] ([172.56.232.151]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-379563e6b6dsm39445329eec.21.2026.11.14.22.05.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Nov 2026 22:05:32 -0800 (PST) Date: Sat, 14 Nov 2026 22:05:28 -0800 From: Chris Down To: Pratyush Yadav Cc: Pasha Tatashin , Mike Rapoport , Andrew Morton , Samiullah Khawaja , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 2/2] mm/memfd_luo: keep memfd frozen until finish In-Reply-To: <20261110175855.2437084-3-pratyush@kernel.org> References: <20261110175855.2437084-1-pratyush@kernel.org> <20261110175855.2437084-3-pratyush@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Message-ID: <20261114220528.f7d9874a014dbb5d@chrisdown.name> User-Agent: Mutt/2.4.3 (cc9e3943) (2026-10-09) X-Spam-Status: No, score=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam09 X-Stat-Signature: 9mfuabez4kpw6ecg6pwuyqt81gnkuxzn X-Rspamd-Queue-Id: C0F2020004 X-Rspam-User: X-HE-Tag: 1794722734-794665 X-HE-Meta: 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 AQTx5hN0 XVozXVeTjvUWnNbeuDWOHM71AwbBgJp/zGzQh+4MnqTpuc/uGv0PNr0d6KppcinGXG47brjwo7+mQoN2Szz4VqhS7ktvmS+GWdKVUx9SrdjqT+LerVJUzi+7bROAA5P8dc8qNeKR6/oFyqewd7NrpEERl+Xncwf0PdJEx1lPHr8rEF+JrUGTmFyvpOdMZJ4YxImpCwa/+Fkog6jDo2aJXnJpq+eMWQi7NuKgRl14LpoEb50mzlC+b4ZbolkUbu0sVsebUCQLkf1iBWAYxC2NKiNhiFLBoIqkp0PZuGeOJihRJEqfDNKb2+lkNiqPQCMNKeK3VIQOCrr1gOg81C/vPwN+e0GsqZqysbgLyb4cOpR7vIzQy/1gaqirn6QqLNhOOmp2NOAsv/LRl3vmQz0KHE44CkcCGLxR02bZ5f0k/oo7nyxnKtkcgCNCNh+5WJUBUVz46O6GsqPEIZBVJLkle5Egj8Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Hi Pratyush, Pratyush Yadav writes: >+ * Restrictions >+ * ============ >+ * >+ * While a memfd is preserved, and after it is retrieved until the session is >+ * finished, its size can't be changed and holes can't be punched in it. >+ * Operations that would do so (``ftruncate()``, ``fallocate()``, writes past >+ * the end of the file) fail. Not a big deal, but there's one more thing that fails in this window and isn't listed here. Adding F_SEAL_WRITE to a retrieved memfd before finish now waits about 150ms and then fails with EBUSY. That's because memfd_wait_for_pins() sees the reference kept from kho_restore_folio() as an extra reference on every folio. Once the session is finished it succeeds straight away. The same already happens while the memfd is preserved in the old kernel, so maybe it's worth mentioning here for both? Also, fallocate() fails with EPERM in every mode while the file is frozen. That includes FALLOC_FL_KEEP_SIZE inside i_size, which neither changes the size nor punches a hole. "Operations that would do so" makes it sound like only some fallocate() calls fail. Otherwise I've tested this across a kexec and it works well. Once those are fixed, please feel free to add: Reviewed-by: Chris Down Tested-by: Chris Down Thanks! Chris